Question 1 of 15
Why are single-phase induction motors not self-starting?
Single-phase induction motors produce a pulsating magnetic field, which doesn't generate a net torque at standstill, preventing self-starting.
Question 2 of 15
What type of supply do single-phase induction motors use?
Single-phase induction motors are designed to operate on a single-phase AC supply.
Question 3 of 15
What is the primary difference in the magnetic field produced by single-phase and three-phase induction motors?
Three-phase motors produce a rotating magnetic field, allowing them to self-start, while single-phase motors produce a pulsating field.
Question 4 of 15
What is the double-revolving field theory used to explain?
The double-revolving field theory explains why single-phase induction motors do not self-start.
Question 5 of 15
According to the double-revolving field theory, how can the pulsating field of a single-phase motor be represented?
The pulsating field can be mathematically resolved into two equal and opposite rotating magnetic fields.
Question 6 of 15
What is the net torque at standstill in a single-phase induction motor, according to the double-revolving field theory?
At standstill, the equal and opposite torques from the two rotating fields cancel each other out, resulting in zero net torque.
Question 7 of 15
Which type of induction motor is inherently self-starting?
Three-phase induction motors are inherently self-starting due to the rotating magnetic field produced by the three-phase supply.
Question 8 of 15
What is the function of an external starting mechanism in a single-phase induction motor?
An external mechanism provides the initial push, allowing the motor to start rotating in one direction.
Question 9 of 15
In a three-phase motor, what is the phase difference between the three phases of the supply?
The three phases are 120 degrees apart.
Question 10 of 15
What does a three-phase supply produce in the rotor?
The three-phase supply creates a rotating magnetic field.
Question 11 of 15
What happens when a three-phase supply is applied to a three-phase induction motor?
The rotating magnetic field causes the rotor to start rotating and the motor to start on its own.
Question 12 of 15
Why is the resultant starting torque zero in a single-phase induction motor?
The alternating current reverses every half cycle, resulting in zero starting torque.
Question 13 of 15
Which theory explains the interaction between the stator's main winding and the rotor's induced currents in a single-phase induction motor?
The cross-field theory explains this interaction.
Question 14 of 15
What is absent in a single-phase induction motor at standstill, according to the cross-field theory?
At standstill, there is no rotor motion to induce currents, so the cross field is absent, preventing self-starting.
Question 15 of 15
What is the nature of the magnetic field produced by the stator's main winding?
The stator's main winding produces a pulsating magnetic field.
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